In Afghanistan, today a man suspected to be an Afghan army officer opened fire on Afghan and NATO troops. He killed an American two-star general, the highest-ranking U.S. officer killed in Afghanistan. NPR has confirmed that he is Major General Harold Greene and that his family has been notified. We'll hear more about Greene in a few minutes. Today's shooting took place at an Afghan Army officer training facility outside Kabul. At least 15 other NATO troops and three Afghans were wounded. NPR's Sean Carberry joins us from Kabul. And Sean, what's the latest information you have about what happened?

SEAN CARBERRY, BYLINE: Well, a delegation of NATO officials were conducting with they call a key leader engagement. It's a typical meeting of high-level NATO officials with Afghan officials. And during the meeting, a man in Afghan army uniform opened fire.

It's unclear at this point whether or not an argument participated or what instigated the shooting. The American general was killed. A German brigadier general was wounded, though not seriously. And the Afghan general who's in charge of the base was reported to be wounded seriously. A number of other U.S. forces were wounded in the attack.

CORNISH: Is any more known about the gunman?

CARBERRY: At this point, no. The Afghan Ministry of Defense is only saying a terrorist dressed in an Afghan uniform was responsible for the shooting. They have not yet confirmed whether he was in fact an active Army officer. The Pentagon has said, they have no reason to suspect that the shooter wasn't. But typically, in this case, they describe the shooter only as wearing a uniform until they're able to confirm whether or not the shooter was an active service member.

CORNISH: In the meantime, have the Taliban claimed credit for the attack?

CARBERRY: They haven't, and in fact, they've been tweeting about it simply as a news story. In past attacks, the Taliban have been very quick to claim credit and highlight the incident as a successful example of their strategy of infiltrating the Afghan forces. So right now, no one knows whether this was part of a militant plan or simply a disgruntled soldier.

And one thing to note is that in the past, the Taliban have been involved in some of the insider attacks, but they've often claimed credit for attacks they had nothing to do with. So again, it's just not clear at this point what was behind this.

CORNISH: Sean, it seems that in the past, these so-called green-on-blue attacks - attacks by Afghan soldiers on NATO forces - were pretty regular occurrence. But they've become increasingly rare. Can you tell us what accounts for that drop?

CARBERRY: Yes, you're right. They have dropped dramatically. The last fatal green-on-blue attack was in February, whereas in 2012, more than 60 NATO service members were killed in more than 40 attacks. And that prompted a number of security changes. NATO forces began carrying loaded magazines in their weapons on bases. They also make sure they had what are called guardian angels watching over meetings with Afghan forces. They even built walls between the Afghan and NATO sides of bases.

But the other factor behind the decline is the fact that there's simply fewer NATO forces in the country now. And with that ongoing drawdown, there's less contact with Afghan forces and fewer opportunities for attacks today.

CORNISH: Still, we should note that there are reports that there was another green-on-blue attack in Afghanistan today. What information do you have about that incident?

CARBERRY: Well, NATO hasn't confirmed that incident yet. But Afghan officials have said that in eastern Paktika province, a guard at the provincial governor's compound got into an altercation with a NATO service member and opened fire. The NATO service member was wounded, and the gunman was shot and later died from his wounds. There's nothing to indicate any connection between these two attacks today, but it is certainly a coincidence, given how rare these insider or green-on-blue attacks have become in recent months.